Osteoarthritis, a common degenerative joint disease, causes substantial morbidity with large attendant economic costs. The biologic or biomechanical processes underlying this disease are largely unknown. Heavy physical loading from work or sports may play a causal role in osteoarthritis. We propose to examine this hypothesis in a retrospective case-control study. The study population will be drawn from the Group Health Cooperative (GHC), a Health Maintenance Organization that provides comprehensive care to approximately 470,000 enrollees. 200 cases will be persons age 50-75 who have undergone hip replacement for idiopathic osteoarthritis; age and sex-matched community controls will be drawn from within GHC. Cases and controls will complete a questionnaire and telephone interview to assess past occupational history and recreational activities. Estimates of static and dynamic physical exposures at the hip will be used to estimate relative risks of disease for different occupational and recreational activities. Specific aims of the study include the following: 1.) To determine if an association exists between severe osteoarthritis and a history of heavy occupational or recreational exposure to static and dynamic loads at the hip. 2.) To assess which occupational or recreational exposures contribute most strongly to any observed risks of severe osteoarthritis. 3.) To determine whether gender and age at exposure modify observed risks for osteoarthritis. 4.) To study the role of body mass index in modifying risk for osteoarthritis. This study will provide important information regarding the role of chronic exposure to heavy physical loads in causing osteoarthritis.